NAME¶

std::map::value_comp - std::map::value_comp

Synopsis¶

std::map::value_compare value_comp() const;

Returns a function object that compares objects of type std::map::value_type
(key-value pairs) by using key_comp to compare the first components of the pairs.

Parameters¶

(none)

Return value¶

The value comparison function object.

Complexity¶

Constant.

Example¶

// Run this code

#include <cassert>
#include <iostream>
#include <map>

// Example module 97 key compare function
struct ModCmp {
bool operator()(const int lhs, const int rhs) const
{
return (lhs % 97) < (rhs % 97);
}
};

int main()
{
std::map<int, char, ModCmp> cont;
cont = { { 1, 'a' }, { 2, 'b' }, { 3, 'c' }, { 4, 'd' }, { 5, 'e' } };

auto comp_func = cont.value_comp();

const std::pair<int, char> val = { 100, 'a' };

for (auto it : cont) {
bool before = comp_func(it, val);
bool after = comp_func(val, it);

std::cout << '(' << it.first << ',' << it.second;
if (!before && !after)
std::cout << ") equivalent to key " << val.first << '\n';
else if (before)
std::cout << ") goes before key " << val.first << '\n';
else if (after)
std::cout << ") goes after key " << val.first << '\n';
else
assert(0); // Cannot happen
}
}

Output:¶

(1,a) goes before key 100
(2,b) goes before key 100
(3,c) equivalent to key 100
(4,d) goes after key 100
(5,e) goes after key 100

See also¶

key_comp returns the function that compares keys
(public member function)